This invention relates to a rotary valve for controlling the supply and discharge of fluid by relatively rotating an input shaft and an output shaft, and a method of assembling the same.
A conventional rotary valve comprises an input shaft rotated by an external operation, an output shaft arranged concentrically with the input shaft, and a torsion bar extending through the input shaft and having first and second ends connected to the input shaft and the output shaft, respectively. When the input shaft and the output shaft rotate relatively, the rotary valve controls the supply and discharge of pressurized fluid. To interconnect the input shaft and the torsion bar of the rotary valve, a central position of the input shaft is detected by turning the input shaft clockwise and counterclockwise relative to the output shaft. The central position is determined such that the characteristics of hydraulic pressure are symmetrical on both sides of the central position. While the relative positions of the input shaft and the torsion bar are kept at the central position, through bores are drilled diametrically in a connecting end of the input shaft and the associated connecting end of the torsion bar. A balance pin is then inserted into the through bores, thus fastening the input shaft and the torsion bar together. To seal the inside of the input shaft airtight, an O ring is attached on the side of the output shaft, distal from the balance pin, which is in the connecting end of the torsion bar.
In the conventional rotary valve, however, the inner diameter of the input shaft is larger in measurement than the outer diameter of the torsion bar, thus a gap exists between the input shaft and the torsion bar at the connecting end. Consequently, the input shaft and the torsion bar are prone to slippage, and the through bores are difficult to drill while the relative position between the input shaft and the torsion bar is maintained at the central position. Furthermore, since the torsion bar is harder than the input shaft, the point of a drill extended through the input shaft is prone to slip on the torsion bar, making the relative position between the input shaft and the torsion bar prone to deviate. Thus the through bores are thus difficult to drill exactly. Additionally, the through bores need to be drilled very carefully so that particles resulting from the drilling operation do not enter the rotary valve. After the through bores are drilled, the rotary valve may require a washing step to remove the particles therefrom, thus making the assembly of the rotary valve intricate. The rotary valve further requires a groove for receiving the O ring, thus further making the assembly intricate. The conventional rotary valve is thus difficult and intricate to assemble.